A rotary combine harvester, hereinafter referred to as a harvester is utilized to harvest crop from a field, separate the grain from the material other than grain (MOG) and to dispense these materials from the machine appropriately. These harvester tasks are complicated and difficult to accomplish. Indeed, not only do they need to be adapted to separate many different types of grains from MOG but they must also account for different crop conditions and weather conditions in which the harvesters must operate in.
A rotary combine harvester's main threshing and separating system consists of a large cylindrical rotor driven by the machines main engine. There are threshing elements attached to the rotor that cooperate with stationary elements, referred to as concaves, that surround the rotor in a rotor cage. Threshing and separating is accomplished by a combination of impact and rubbing action. As the rotor rotates, the grain crop is forced through a gap between the rotor and the concaves and begins a spiral path through the front (threshing) section and then through the rear (separating) section towards the exit area of the rotor/concave system. The impact and rubbing action causes the grains to be detached. By the time the crop is at the exit area almost all the grain has been separated from the MOG. The term for any grain that is remaining is called rotor loss. There are also other losses that can be attributed to the rotor/concave system, this is known as damaged grain loss (broken or cracked kernels).
As with any machine, performance is the key to efficiency. As mentioned above, performance of the threshing mechanisms is measured by: Threshing efficiency; Separating efficiency; and Grain damage. The machine operator has several means to adjust the threshing/separating efficiency vs. grain damage equation. The speed at which the rotor turns (RPM) is adjustable, the gap between the rotor and the concaves is adjustable, and the crop feed rate can be adjusted simply by running more or, less material into the machine. Also, the condition of the crop itself can have a dramatic effect on the loss vs. damage ratio. Crop moisture content, crop maturity, and crop type profoundly affect the machine performance. Along with all these variables and possible adjustments, the operator still might not get the machine to perform to acceptable levels. At this point the owner or operator may start looking at threshing/separating components they might install in place of conventional components.
Typically, new rotary combine harvesters will have installed a standard set of concaves, depending on the original equipment manufacturer. Present difficulties with current designs include concaves which cause excessive grain damage as the crop material continues its spiral flow.